1. Field of the Invention
The present invention relates to a printing method comprising the steps of developing a planographic printing plate, adhering ink to the planographic printing plate, and transferring the ink to a printing target, and to a planographic printing plate which has been processed by the above printing method.
2. Description of the Related Art
In the recent plate-making method (including xerographic plate-making method), in order to facilitate automation of a plate-making process, a planographic printing plate such as a photosensitive printing plate or a heat-sensitive printing plate is widely used. Generally, the planographic printing plate is manufactured such that surface treatments such as a graining treatment, an anodic oxidation treatment, a silicate treatment, and a chemical conversion treatment are conducted on a support such as a sheet-type or coiled aluminum plate singly or appropriately in combination. Then, the surface-treated support is coated with a photosensitive layer or a heat-sensitive layer (which is collectively referred to as a xe2x80x9ccoating filmxe2x80x9d, and a surface applied with the coating film is referred to as an xe2x80x9cimage forming surfacexe2x80x9d, a surface unapplied with the coating film is referred to as a xe2x80x9cnon-image forming surfacexe2x80x9d).
The planographic printing plate is subjected to image-forming treatments such as an exposure treatment, a development treatment, and a gumming treatment. The planographic printing plate for which the image-forming treatments have been completed is set in a printer, and then ink is applied thereto. Accordingly, characters, images and the like are printed on a paper surface which is a printing target.
If the printing target is large (as in a case of a newspaper or the like, for example), there is a case of using the planographic printing plate which is smaller than the printing target. In this case, since an edge of the planographic printing plate is located at the inner side of that of the printing target, if ink is unexpectedly deposited on the edge portion of the planographic printing plate, the ink is transferred onto the printing target, whereby so-called xe2x80x9cedge-stainxe2x80x9d is caused. If the edge-stain is produced, dots or lines appear at portions other than characters or patterns that should be primarily printed, whereby printing quality of the printing target deteriorates.
In order to prevent such edge-stain as described above, a method in which edge portions (corner portions) of an aluminum support of the planographic printing plate are shaved off by a file or knife is disclosed in Japanese Patent Application (Laid-Open) JP-A No. 59-97146. In this way, if the edge portions of a planographic printing plate are shaved, the edge portions do not come into contact with the printing target, and ink depositing on the edge portions is not transferred onto the printing target, whereby edge-stain can be prevented.
An operation of shaving off the edge portions of the planographic printing plate involves shaving off an aluminum support, which requires lots of time and labor. Further, since the edge portions must be shaved off for each of the planographic printing plates which have been cut to a desired size, if the edge portions of supports of a great number of the planographic printing plates are shaved off, further more time and labor are required.
It is possible to carry out the shaving-off operation on the edge portions of the planographic printing plate on a general processing line thereof. However, a cutting slitter or cutter must be switched to another one as necessary (or based on the size of the planographic printing plate). Before or after the switching operation, some of the planographic printing plates may become unavailable as products, leading to the waste of materials for the planographic printing plates. In addition, during the switching operation, since the processing line must be stopped, it becomes impossible to process the planographic printing plates, thus wasting time.
In view of the foregoing, an object of the present invention is to provide a printing method of a planographic printing plate and a planographic printing plate processed by this method, which is able to ensure that edge-stain can be prevented without requiring much time and labor.
In order to accomplish the above-described objects, the present invention provides a method for printing, comprising the steps of: a) developing an image forming surface of a planographic printing plate; b) after the developing, hydrophilizing a portion of a vicinity of an edge of the image forming surface; c) after the hydrophilizing, adhering ink to the image forming surface; and d) transferring the ink to a printing target.
In the present invention, the step of hydrophilizing is conducted on the portion in the vicinity of the edge of the image forming surface of the planographic printing plate for which the step of developing has been completed and for which the step of adhering ink is not completed. Thereafter, the image forming surface of the planographic printing plate is deposited with ink. The ink is transferred, for example, onto a rubber blanket and then transferred to the printing target such as paper (otherwise, the ink may be directly transferred onto the printing target). Ink does not easily deposit on the portion in the vicinity of the edge of the image forming surface (preferably, ink never deposits on the portion in the vicinity of the edge), whereby edge-stain is prevented from being produced on the printing target.
In the present invention, since a shaving-off operation of portions of the support of the planographic printing plate is not required and the developed planographic printing plate can be used in a printer as it is, time and labor can be saved. Further, since it is not necessary to carry out a switching operation on the processing line of the planographic printing plate, materials for the planographic printing are not wasted.
In printing using the planographic printing plate, there is a case in which a gum solution is applied to the developed planographic printing plate. In this case, the step of hydrophilizing can be performed after or before the step of applying the gum solution. Generally, since the step of developing and the step of applying the gum solution are often conducted by one developing apparatus (printing processor in a broad sense), when the step of hydrophilizing is conducted after the step of applying the gum solution, the conventional developing apparatus need not be modified and can be used as it is. On the contrary, there is a case in which it is considered to be preferable to apply the gum solution to the planographic printing plate which has been hydrophilized. Accordingly, in this case, if a system is adopted in which the step of hydrophilizing is conducted before the step of applying the gum solution (i.e., the planographic printing plate is developed, hydrophilized, and applied with the gum solution), the number of steps in the entire printing can be reduced a great deal.
A portion to be hydrophilized is not limited as long as edge-stain is not produced in the portion. However, for example, it is preferable that a width of the portion to be hydrophilized is no more than 3 mm from the edge of the image forming surface of the planographic printing plate. Namely, if the width of the portion to be hydrophilized is no more than 3 mm, a broad region for forming an image can be secured.